Intro to General Chemistry: Foundational Concepts and Measurements

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Intro to General Chemistry

Classification of Matter

The study of chemistry begins with understanding matter and its changes. Matter is anything that occupies space and has mass. It can be classified into different types based on its composition and properties.

Pure Substance: Matter composed of only one kind of atom or molecule. Examples include elements and compounds.
Mixture: Matter composed of two or more different elements or compounds that are physically mixed together but not chemically bonded.

Classification of Matter Table:

Type	Description	Example
Element	Single type of atom	Gold (Au)
Compound	Two or more atoms chemically bonded	Water (H2O)
Homogeneous Mixture	Uniform composition throughout	Salt water
Homogeneous Mixture	Non-uniform composition	Salad

Example: Crystalline sugar is a pure substance; salsa is a heterogeneous mixture.

Physical and Chemical Changes

Changes in matter can be classified as physical or chemical. Physical changes affect the state or appearance without altering composition, while chemical changes result in new substances.

Physical Change: Change in physical state or appearance (e.g., melting, dissolving).
Chemical Change: Change in chemical composition, forming new substances (e.g., burning, rusting).

Phase Changes: Transitions between solid, liquid, and gas states are physical changes. Examples include melting, freezing, and boiling.

Reversible Change: Can be undone (e.g., melting ice).
Irreversible Change: Cannot be undone (e.g., burning wood).

Example: Dissolving sugar in water is a physical change; burning wood is a chemical change.

Chemical and Physical Properties

Properties of matter are divided into chemical and physical properties.

Chemical Property: Observed during a chemical reaction (e.g., flammability, reactivity).
Physical Property: Measured without changing chemical identity (e.g., color, melting point).

Example: Mercury is a silvery liquid at 25°C (physical property); sodium reacts violently with water (chemical property).

Intensive vs. Extensive Properties

Properties are further classified based on their dependence on the amount of substance.

Intensive Property: Independent of amount (e.g., density, boiling point).
Extensive Property: Dependent on amount (e.g., mass, volume).

Example: Density is intensive; mass is extensive.

Temperature and Thermal Energy

Temperature measures the average kinetic energy of particles in a substance. Thermal energy is the total kinetic and potential energy of all atoms in an object.

Temperature Units: Celsius (°C), Kelvin (K), Fahrenheit (°F)

Temperature Conversion Formulas:

Example: If the melting point of phosphorus is 44.1°C, it would exist as a solid at 128°F.

Scientific Notation

Scientific notation is used to express very large or small numbers in a compact form.

Format: , where and is an integer.
Example:

Conversion: Move the decimal point to create a coefficient between 1 and 10, adjusting the exponent accordingly.

SI Units and Measurements

The International System of Units (SI) is the standard for scientific measurements.

Physical Quantity	Unit	Symbol
Length	meter	m
Mass	kilogram	kg
Time	second	s
Temperature	kelvin	K
Amount of substance	mole	mol

Area and Volume:

Area:
Volume (cube):

Metric Prefixes

Metric prefixes are used to indicate multiples or fractions of base units.

Prefix	Symbol	Multiplier
kilo	k
centi	c
milli	m
micro	μ

Example: 654 kg to g: g

Significant Figures

Significant figures indicate the precision of a measurement.

All nonzero digits are significant.
Zeros between nonzero digits are significant.
Leading zeros are not significant; trailing zeros are significant only if there is a decimal point.

Example: 0.00364 has 3 significant figures.

Precision in Measurements

When recording measurements, include all certain digits plus one estimated digit.

Example: Measuring length with a ruler to the nearest 0.01 cm.

Significant Figures in Calculations

Multiplication/Division: Result has the same number of significant figures as the value with the fewest significant figures.
Addition/Subtraction: Result has the same number of decimal places as the value with the fewest decimal places.

Example:

Conversion Factors

Conversion factors are ratios used to convert between units.

Example: 1 day = 24 hours
Common conversion factors include length, mass, and volume units.

Quantity	Conversion Factor
Length	1 in = 2.54 cm
Mass	1 kg = 1000 g
Volume	1 L = 1000 mL

Dimensional Analysis

Dimensional analysis is a method for converting units using conversion factors.

Set up the problem so that units cancel, leaving the desired unit.
Example: To convert 32 inches to centimeters, use

Density

Density is the amount of mass per unit volume.

Formula:
Units: g/cm3 for solids and liquids, g/L for gases

Example: If a metal has a density of 2.14 g/cm3, its density in kg/m3 is kg/m3

Density of Geometric Objects

For regular shapes, use geometric formulas to find volume and then calculate mass using density.

Cube:
Sphere:
Cylinder:

Example: A cube with sides of 3.0 cm and density 10.5 g/cm3 has mass g

Density of Non-Geometric Objects: Water Displacement

Water displacement is used to measure the volume of irregularly shaped objects.

Volume displaced = Final water level - Initial water level

Example: If water rises from 200 mL to 265 mL, the object's volume is 65 mL.

Additional info: These notes cover foundational concepts in general chemistry, including matter classification, properties, measurement, and calculation techniques essential for laboratory and theoretical work.